The field is reduction of noise, vibration, and harshness (NVH) in an opposed-piston engine. More specifically, the field covers controlling backlash in the gear train of an opposed-piston engine with a split gear construction.
Gear vibration and clash in an internal combustion engine of a vehicle lead to intense whining and/or sharp impulse noise which can cause operator and passenger discomfort. Engine whine and rattle also add to the constant cacophony that makes proximity to transportation routes and industrial sites very unpleasant. Consequently, performance standards and environmental regulations relating to engines increasingly include NVH limits.
When gears interface with each other, there are usually gaps between the interfacing gear teeth. As the gears rotate, these gaps are closed when the teeth move to make contact, which can result in gear rattle. In some instances, the space is called backlash; in other instances the movement made to close the gaps is called backlash. In either case, it is desirable to control, reduce, or eliminate backlash.
The gear train of an opposed-piston engine with dual crankshafts inherently experiences torque reversals. In the case where a phase difference is provided between the crankshafts in order to differentiate port opening and closing times, the gear train is subjected to multiple torque reversals during every cycle of engine operation. With backlash, the engine's operation is afflicted with audible clatter and hammering as instantaneous accelerations caused by the reversals cascade through the gear train. Even without an inter-crankshaft phase difference, momentary inter-gear torque reversals result from idler bounce and/or gear/shaft rotational distortion.
The well-known split gear construction provides an underpinning for various solutions to gear train backlash. In a split gear construction, two or more gears are arranged in an abutting, face-to-face relationship on a common shaft or post so as to act as a single gear. Various means are employed to impose and maintain a rotational offset between the gears by a distance amounting to some fraction of a gear tooth. The relative movement effectively increases the width of the split gear's teeth, thereby closing interstitial space between meshed gear teeth. Some of these split gear constructions use bias members such as springs that continuously act between the gears so as to maintain a rotational offset that varies in response to rotation of the gear and to sporadic accelerations caused by torque reversals, etc. The rotational offset automatically moves the gears to maintain closure of the gaps between meshed gear teeth. See, for example, U.S. Pat. No. 2,607,238 and U.S. Pat. No. 3,174,356. Because the resulting back-and-forth movements of the split gear teeth resemble the opening and closing actions of scissor blades, these gears may also be called “scissor gears”. In this regard, see US publication 20110030489.
In related U.S. application Ser. Nos. 13/944,787 (Pre-Grant Publication US 2015/0020627) and 14/074,618 (Pre-Grant Publication US 2015/0020629) split gear constructions include combinations of compliant and stiff gears. The compliant gears receive the torque load first and slightly deform as the stiff gears begin to absorb the gear loads. As a compliant gear deforms, a stiff gear increasingly absorbs torque loads, which are transmitted via friction between compliant and stiff gears. Consequently, only a compliant gear transfers the total torque load to a hub thereby reducing or eliminating gear backlash.
The spring-biased split gear constructions are intended to automatically eliminate backlash by relative rotation between the two gears in opposing directions. Thus, as a succession of torque reversals occurs, slack is taken up by a succession of rotational adjustments of the split gears. This results in a continuous back-and-forth movement of the gears that causes wear of the gear parts and consumes energy. The split gear constructions of the related applications depend on the availability of compliant materials which may be in short supply, or, if available, unsuited to particular applications. Therefore, it is desirable to have spring-biased gear constructions with anti-backlash capability available that reduce wear, conserve energy, and operate well in a broad range of applications.
According to this disclosure the technological problem of backlash in the gear train of an opposed-piston engine is solved with a split gear construction that achieves wear reduction, energy conservation, and good operation in a broad range of applications. In this construction, relative rotation between two gears of a split gear assembly is allowed in a first direction, but constrained in the second direction. A first gear of the split gear is automatically rotated with respect to the second gear in the first direction until it contacts one flank of a tooth groove in a mating gear. At this point the second gear is in contact with the opposite flank of the tooth groove and backlash is reduced, if not eliminated, as the split gear rotates. When torque reversal occurs, the counter-rotation constraint keeps the two gears locked in their previously-rotated positions and no backlash is available.